Radio communication systems, such as the Global System for Mobile Communication (GSM) or the Universal Mobile Telecommunications System (UMTS), generally includes a core network (CN) and a radio access network (RAN). The core network provides services, such as routing phone calls, to user equipment (UE) connected by the radio access network (RAN). The core network includes inter-connected nodes known as Mobile Switching Center (MSC) servers (MSS or MSC server). The radio access network includes base station controllers/radio network controllers (BSCs/RNCs).
The core network architecture is divided into a call control layer and a connectivity layer. An MSC server is implemented in the control layer, and is responsible for signaling traffic (e.g., call set up, charging, etc.) and controlling Media Gateways (MGWs). Media gateways are implemented in the connectivity layer where all user data is transported, routed and switched, and are responsible for handling the bearer traffic according to instructions from an MSC server. An MSC server is usually located at a central site for signaling and managing Media gateways, while Media gateways are usually deployed at remote sites and at interconnection points with other mobile and fixed networks.
Several MSC servers can be connected together to form a MSC server pool (or MSS pool), whereby all MSC servers within the pool operate together to handle the traffic load in the network. In the MSS pool architecture, each MSC server in the pool is connected to all base station controller/radio network controllers, such that each MSC server node shares the same service area as the other MSC server nodes in the same pool. The MSS pool architecture, also known as lu-flex (Wideband Code Division Multiple Access (WCDMA)) or A-Flex (GSM), conforms to the 3GPP TS 23.236 specification for Intra Domain Connection of RAN Nodes to Multiple CN Nodes. Media gateways support MSS pooling through a feature known as the Virtual Media Gateway (vMGW) that allows all MSC servers in the pool to use the resources in one physical MGW.